1. Field of the Invention
The present invention relates to a silicon carbide substrate, an epitaxial wafer and a manufacturing method of a silicon carbide substrate.
2. Description of the Background Art
Silicon carbide (SiC) has a large band gap, and a maximum insulation breakdown electric field and thermal conductivity thereof are larger than those of silicon (Si). However, a mobility of carriers of the silicon carbide is substantially similar to that of the silicon, and a saturation drift velocity of electrons and a breakdown voltage of the silicon carbide are large. Therefore, it has been expected to apply it to semiconductor devices that are required to have higher efficiency, high breakdown voltage and large capacity.
Many defects such as micropipes are present in an SiC substrate used in the SiC semiconductor device. Therefore, researches have been made on conditions and the like of epitaxial growth for removing the effects existing in the SiC substrate by the epitaxial growth (e.g., Japanese Patent Laying-Open No. 2000-26199 (Patent Document 1), Japanese Patent Laying-Open No. 2003-332562 (Patent Document 2) and Japanese Patent Laying-Open No. 2007-269627 (Patent Document 3)).
In general, the SiC substrates are manufactured by forming an SiC ingot, cutting the SiC ingot into the SiC substrates and polishing them. According to the above patent documents 1 to 3, however, an abrasive liquid used for manufacturing the SiC substrate, a fixing agent for fixing the SiC substrate during the polishing and the like are left as adhered residues. The inventors have found that defects due to these residues are formed in an epitaxial layer when the epitaxial layer is formed on the SiC substrate carrying the residues adhered thereto. When the epitaxial layer containing such defects is used in the semiconductor device, operations of the semiconductor device are adversely affected.